The present invention relates to a technique to drive a solid state imaging apparatus, and more particularly, it relates to a driving technique for realizing an electronic shutter function in a solid state imaging apparatus.
An electronic shutter function in a solid state imaging apparatus is a function for adjusting a charge storage time in an imaging unit so as to electronically control an exposure time in place of a physical diaphragm function. Specifically, the electronic shutter function can be realized by discharging (resetting) a signal charge stored in each pixel at a predetermined timing different from a timing for reading a pixel signal.
In other words, in order to realize the electronic shutter function in a solid state imaging apparatus, a peripheral circuit is required to have a configuration where the imaging unit can be accessed for resetting at a timing independent of a timing for making an access for reading a pixel signal. Accordingly, a conventional solid state imaging apparatus includes a row selecting shift register for the electronic shutter function in addition to a row selecting shift register for reading a pixel signal, so as to make an access to the imaging unit for resetting by using this additional row selecting shift register. Thus, the electronic shutter function is realized in the conventional solid state imaging apparatus.
The conventional solid state imaging apparatus with the electronic shutter function has, however, the following problems:
Since a shift register occupies a comparatively large area in the entire layout of the solid state imaging apparatus, the two row selecting shift registers provided in the conventional solid state imaging apparatus can be an obstacle to downsizing and cost reduction. Moreover, since the two shift registers are independently driven, the power consumption is accordingly increased. Therefore, the two shift registers are not desirable also in view of reduction of power consumption.
The object of the invention is realizing, in a solid state imaging apparatus, both a normal function to read a pixel signal and an electronic shutter function by using a single shift register.
Specifically, the solid state imaging apparatus of this invention comprises an imaging unit including two-dimensionally arranged plural pixels; a shift register containing plural serially connected registers including registers respectively corresponding to rows or columns of the imaging unit for successively transmitting a supplied driving signal in accordance with each clock; and a driver unit including plural selecting circuits provided correspondingly to the rows or columns of the imaging unit in the same number as the number of the rows or columns, for executing a read operation or a reset operation in pixels belonging to a row or column selected in accordance with an output of a register included in the shift register, wherein each of the selecting circuits receives an output of one register, among the registers of the shift register, corresponding to a row or a column corresponding to the selecting circuit and an output of another register disposed away from the corresponding register by a predetermined number of stages in the shift register, and when the output of the corresponding register is the driving signal, selects a read operation or a reset operation in accordance with the output of the latter register and executes the selected operation in the pixels of the corresponding row or column.
In this solid state imaging apparatus, when the driving signal is output from one register included in the shift register and disposed correspondingly to a row or column of the imaging unit, the selecting circuit corresponding to that row or column selectively executes a read operation or a reset operation in the pixels of the row or column in accordance with the output of another register disposed away from the corresponding register by a predetermined number of stages in the shift register. Accordingly, by setting the supply of the driving signal to the shift register so that, when one register outputs the driving signal, the output of another register can be different between the normal mode for reading a pixel signal and the electronic shutter mode, a read operation and a reset operation can be selectively executed in the imaging unit in the normal mode and the electronic shutter mode, respectively. Therefore, the normal function to read a pixel signal and the electronic shutter function can be both realized by using one and the same shift register.
In the solid state imaging apparatus, the latter register is preferably disposed in a stage at least preceding to or following the corresponding register in the shift register. In this manner, each selecting circuit can receive the output of the register corresponding to the row or column corresponding to the selecting circuit and the output of another register disposed in a stage at least preceding to or following the corresponding register, namely, the selecting circuit can receive the outputs of the registers in two or three stages. Thus, the configuration of a driver unit can be simplified.
Also, the solid state imaging apparatus can further comprise a control unit for controlling supply of the driving signal to the shift register, and the control unit preferably controls the driving signal to be supplied to the shift register in one clock period when one of a normal mode for reading a pixel signal and an electronic shutter mode is specified and to be supplied to the shift register in at least two clock periods when the other mode is specified.
In this manner, the driving signal is supplied in one clock period in one of the normal mode and the electronic shutter mode and in at least two clock periods in the other mode. Accordingly, when the driving signal is output from one register, none of the other registers outputs the driving signal in one mode, and any of the other registers outputs the driving signal in the other mode. As a result, each of the selecting circuits can easily selectively execute a read operation or a reset operation in accordance with the presence of the driving signal output from another register.
Furthermore, in the solid state imaging apparatus, each of the selecting circuits can include a combinational circuit for receiving the output of the corresponding register and outputs of other registers disposed in preceding and following stages of the corresponding register, and in the case where the driving signal is output from the corresponding register, when any of the other registers outputs the driving signal, the selecting circuit executes one of the read operation and the reset operation, and when none of the other registers outputs the driving signal, the selecting circuit executes the other operation.
Alternatively, the method of this invention of driving a solid state imaging apparatus including an imaging unit containing two-dimensionally arranged plural pixels and a shift register containing plural serially connected registers including registers respectively corresponding to rows or columns of the imaging unit, comprises a first step of supplying a driving signal to the shift register; a second step of detecting, among the registers included in the shift register, a register outputting the driving signal; and when one register is detected to output the driving signal in the second step, a third step of selecting a read operation or a reset operation in accordance with an output of another register disposed away from the detected register by a predetermined number of stages in the shift register, and executing the selected operation in pixels belonging to a row or column corresponding to the detected register.
In this method, when one register is detected to output the driving signal, a read operation or a reset operation is selectively executed in the pixels belonging to a row or column corresponding to the detected register in accordance with the output of another register disposed away from the detected register by a predetermined number of stages in the shift register. Accordingly, by setting the supply of the driving signal to the shift register so that, when one register outputs the driving signal, the output of another register can be different between the normal mode for reading a pixel signal and the electronic shutter mode, a read operation and a reset operation can be selectively executed in the imaging unit in the normal mode and the electronic shutter mode, respectively. Therefore, the normal function to read a pixel signal and the electronic shutter function can be both realized by using one and the same shift register.
In this method, the latter register is preferably disposed in a stage at least preceding to or following the detected register in the shift register.
Furthermore, in the first step, when one of a normal mode for reading a pixel signal and an electronic shutter mode is specified, the driving signal is preferably supplied to the shift register in one clock period, and when the other mode is specified, the driving signal is preferably supplied to the shift register in at least two clock periods.
In this manner, the driving signal is supplied to the shift register in one clock period in one of the normal mode and the electronic shutter mode, and in at least two clock periods in the other mode. Accordingly, when the driving signal is output from one register, none of the other registers outputs the driving signal in one mode, and any of the other registers outputs the driving signal in the other mode. Therefore, a read operation or a reset operation can be easily selectively executed in accordance with the presence of the driving signal output from another register.